Highly corrosion-resistant Ni-Cr-Mo-N alloy having superior phase stability

Abstract

A highly corrosion-resistant Ni—Cr Mo—N alloy including in weight %, Ni: 22.0% or more, Cr: 22.0% or more, Mo: 5.0% or more, N: 0.180% or more, Si, Al, Mn, Fe as a remainder, and inevitable impurities, wherein the composition satisfies the following Formulas (1) to (3), and an area ratio of a sigma phase in a cross-sectional structure measured by EBSD after holding at 950° C. for 30 minutes is 1.0% or less Cr+3.3×Mo+16×N≥43.0  (1) 7.3×Mo—Ni≤21.0  (2-1) 1.3×Cr—Ni≤5.7  (2-2) 1.6×Si+0.99×Mn+2.2×Al≤0.95  (3).

The invention claimed is: 
     
         1 . A Ni—Cr Mo—N alloy consisting of, in weight %,
 C: 0.001 to 0.030%, 
 Si: 0.02 to 0.30%, 
 Mn: 0.02 to 0.40%, 
 P: 0.005 to 0.050%, 
 S: 0.0001 to 0.0030%, 
 Ni: 22.0 to 38.0, 
 Cr: 22.0 to 28.0, 
 Mo: 5.0 to 8.0%, 
 Cu: 0.02 to 0.45%, 
 N: 0.180 to 0.250%, 
 Al: 0.005 to 0.100%, 
 Fe as a remainder, and inevitable impurities, 
 wherein the composition satisfies the following Formulas (1) to (3);
   Cr+3.3×Mo+16×N≥43.0  (1)
 
   7.3×Mo—Ni≤21.0  (2-1)
 
   1.3×Cr—Ni≤5.7  (2-2)
 
   1.6×Si+0.99×Mn+2.2×Al≤0.95  (3), and
 
 
 an area ratio of a sigma phase in a cross-sectional structure measured by EBSD after holding at 950° C. for 30 minutes is 1.0% or less. 
 
     
     
         2 . A sheathed heater comprising a cladding tube composed of the alloy according to  claim 1  and a junction formed with a Ni brazing material. 
     
     
         3 . A Ni—Cr Mo—N alloy consisting of, in weight %,
 C: 0.001 to 0.030%, 
 Si: 0.02 to 0.30%, 
 Mn: 0.02 to 0.40%, 
 P: 0.005 to 0.050%, 
 S: 0.0001 to 0.0030%, 
 Ni: 22.0 to 38.0, 
 Cr: 22.0 to 28.0, 
 Mo: 5.0 to 8.0%, 
 Cu: 0.02 to 0.45%, 
 N: 0.180 to 0.250%, 
 Al: 0.005 to 0.100%, 
 B: 0.0005 to 0.0050%, 
 O: 35 ppm or less, 
 Fe as a remainder, and inevitable impurities, 
 wherein the composition satisfies the following Formulas (1) to (4):
   Cr+3.3×Mo+16×N≥43.0  (1)
 
   7.3×Mo—Ni≤21.0  (2-1)
 
   1.3×Cr—Ni≤5.7  (2-2)
 
   1.6×Si+0.99×Mn+2.2×Al≤0.95  (3)
 
   0.20≤1.6×Si+0.99×Mn+2.2×Al≤0.95  (4), and
 
 
 an area ratio of a sigma phase in a cross-sectional structure measured by EBSD after holding at 950° C. for 30 minutes is 1.0% or less. 
 
     
     
         4 . A sheathed heater comprising a cladding tube composed of the alloy according to  claim 3  and a junction formed with a Ni brazing material.